Electromagnetic and its combined surveying apparatus and method

Abstract

An electromagnetic and its combined surveying apparatus and method, utilizing small-sized one or three-dimensional magnetic field sensors with high dynamic range and high sensitivity, which can be used together with highly populated receivers for the electromagnetic exploration. The electrical field could be derived from the vertical component of the magnetic field of the highly populated receivers and the magneto-telluric data could be derived by measuring the three components of the magnetic data. Moreover, by means of connecting the same populated receivers with geophones or MEMS accelerometers, and moving the seismic sources together with the mobile electromagnetic source, seismic survey could be carried out. It is therefore able to undertake the interpretation of the seismic, electromagnetic and magneto-telluric data and perform a combined field exploration.

What is claimed is: 
     
       1. An electromagnetic and its combined surveying apparatus by means of electromagnetic exploration or combined magneto-telluric and seismic exploration; said apparatus comprising:
 a plurality of receivers distributed over the area to be explored, each of which is connected with at least one of a one-component or three-component portable magnetic field sensor, geophones or MEMS (Micro Electro-Mechanical System) accelerometers, and at least a pair of electrodes, for receiving and recording the one or three-dimensional magnetic field data from the magnetic field sensor, and/or seismic data from the geophones or MEMS accelerometers, and/or electric field data from the pair of electrodes; and 
 a plurality of mobile actuate electromagnetic and/or seismic sources, moved in the vicinity of the receivers or rolled together with the receivers for emitting electromagnetic signals and/or seismic signals, 
 wherein each portable magnetic field sensor includes a first magnetic field sensing unit and a second magnetic field sensing unit; the first magnetic field sensing unit has narrow magnetic field range and high sensitivity and is measured under the condition that the background magnetic field is canceled; the second magnetic field sensing unit has wide magnetic field range and low sensitivity and is used for producing currents flowing through a loop to cancel the background magnetic field at location of the first magnetic field sensor. 
 
     
     
       2. The apparatus as claimed in  claim 1 , wherein the receivers are respectively connected with a one-component or three-component portable magnetic field sensor and one or two pairs of electrodes; and each mobile actuate electromagnetic source is an electromagnetic loop source and/or grounded wire source. 
     
     
       3. The apparatus as claimed in  claim 1 , wherein each of the mobile actuate electromagnetic sources further comprises a loop, a generator, a transformer, a plurality of capacitor banks, and a high current pulse waveform generator. 
     
     
       4. The apparatus as claimed in  claim 3 , wherein the high current pulse waveform generator further comprises a central processing unit capable of generating pulse width modulation, and a plurality of drivers for driving a plurality of insulated gate bipolar transistors so as to drive big current into the loop and to generate different pulse widths with different ramp times. 
     
     
       5. The apparatus as claimed in  claim 3 , wherein the loop further comprises wires or metal rods connected end by end. 
     
     
       6. The apparatus as claimed in  claim 3 , wherein the high current pulse waveform generator is used for generating current waveforms with different controlled pulse widths and ramp times in accordance with different desired depths of penetration. 
     
     
       7. The apparatus as claimed in  claim 3 , wherein the high current pulse waveform generator is used for generating current waveforms with different controlled pulse widths and ramp times using the same capacitor banks by scaling down or up proportionally the current amplitude with respect to the ramp time. 
     
     
       8. The apparatus as claimed in  claim 3 , wherein each of the mobile actuate electromagnetic sources is used to generating current waveforms with different controlled pulse widths and ramp times in accordance with different desired depths of penetration at a fixed location. 
     
     
       9. The apparatus as claimed in  claim 1 , wherein the receivers are arranged in a high-density way sufficient to derive the electrical field from the vertical component of the magnetic field and are placed for a period of time in order to obtain the magneto-telluric data from the three-component magnetic field data. 
     
     
       10. The apparatus as claimed in  claim 1 , wherein at least two mobile actuate electromagnetic sources are linked in parallel and synchronized to increase output power. 
     
     
       11. The apparatus as claimed in  claim 1 , wherein the first magnetic field sensing unit is connected with a magnetic flux concentrator so as to enhance the sensitivity of the first magnetic field sensing unit. 
     
     
       12. The apparatus as claimed in  claim 1 , wherein the second magnetic field sensing unit creates negative background magnetic field by creating the current flowing through a coil, and the coil is a Helmholtz coil, a Solenoid coil, a loop wire, or a wire. 
     
     
       13. The apparatus as claimed in  claim 1 , wherein the total magnetic field for the component in the direction measured is the background magnetic field created by the second magnetic field sensor plus the field measured by the first magnetic field sensor; the background magnetic field is calculated by measuring the current flowing through the coil. 
     
     
       14. The apparatus as claimed in  claim 1 , wherein the first and the second magnetic field sensor are a coil-type magnetic field sensor, a magnetic tunnel junction sensor, or a magneto impedance sensor. 
     
     
       15. An electromagnetic and its combined surveying method, comprising steps of:
 distributing a plurality of receivers over the area to be explored; 
 connecting each receiver with at least one of a one-component or three-component portable magnetic field sensor, geophones or MEMS (Micro Electro-Mechanical System) accelerometers, and at least a pair of electrodes, for receiving and recording the one or three-dimensional magnetic field data from the magnetic field sensor, and/or seismic data from the geophones or MEMS accelerometers, and/or electric field data from the pair of electrodes; and 
 moving a plurality of mobile actuate electromagnetic and/or seismic sources in the vicinity of the receivers or rolled together with the receivers for emitting electromagnetic signals and/or seismic signals, 
 wherein the receivers are respectively connected with a one-component or three-component portable magnetic field sensor and one or two pairs of electrodes, and each mobile actuate electromagnetic source is an electromagnetic loop source; the receivers are arranged in plural rows and rolled over in a certain direction by rolling the last row to the first row heading that direction in order to receive and record magnetic field and electric field data continuously; the electromagnetic loop sources are moved in above rolling direction and actuated to emit electromagnetic signals at a pre-scheduled time or at synchronized time from the radio frequency signal sent by a central controlling center. 
 
     
     
       16. The method as claimed in  claim 15 , wherein the receivers are respectively connected with a one-component or three-component portable magnetic field sensor and one or two pairs of electrodes, and are distributed in the area to be explored at fixed locations for a period of time in order to receive and record magnetic field and electric field data continuously; and each mobile actuate electromagnetic source is an electromagnetic loop source and/or grounded wire source, and is movable so as to be arranged at different locations for transmission. 
     
     
       17. The apparatus as claimed in  claim 15 , wherein the receivers are arranged in a high-density way sufficient to derive the electrical field from the vertical component of the magnetic field and are placed for a period of time in order to obtain the magneto-telluric data from the three-component magnetic field data.